Laser-ablated Be atoms, cations, and electrons were reacted with F2, ClF, Cl2, NF3, CCl4, CF2Cl2, HCl, DCl, and SiCl4 diluted in noble gases. The major products were the dihalides BeF2, BeClF, BeCl2, and the hydride chloride HBeCl, whose identities were confirmed by comparison with previous evaporative work, deuterium substitution, and vibrational frequency calculations. The matrix-isolated fundamental frequency of the BeF molecule is higher, and the frequency of BeCl is lower, than that determined for the gas-phase molecules. The BeF+ and BeCl+ cations formed strong dipole-induced dipole complexes in solid Ne, Ar, Kr, and Xe with stepwise increase in computed noble gas dissociation energies. Going down the family NgBeF+ and NgBeCl+ series (Ng = Ne, Ar, Kr, Xe) the Mulliken charges q(Be) decrease, while q(Ng) increases, and the dipole moments decrease, which suggests covalent bonding in the xenon species. We find that the largest intramatrix shift is Ne to Ar which follows the largest factor increase for the Ng atomic polarizabilities. Extra electrons produce Cl–, which reacts with HCl to form the stable HCl2– anion and possibly with BeCl2 to give BeCl3–. A weak band observed in neon experiments with F2 is probably due to BeF3–.

Infrared spectra of matrix isolated dibridged Si(μ-H)2MH2 and tribridged Si(μ-H)3MH molecules (M = Zr and Hf) were observed following the laser-ablated metal atom reactions with SiH4 during condensation in excess argon and neon, but only the latter species was observed with titanium. Assignments of the major vibrational modes, which included terminal MH, MH2 and hydrogen bridge Si–H–M stretching modes, were confirmed by the appropriate SiD4 isotopic shifts and density functional vibrational frequency calculations (B3LYP and BPW91). The Si–H–M hydrogen bridge bond is calculated as weak covalent interaction and compared with the C–H···M agostic interaction in terms of electron localization function (ELF) analysis and noncovalent interaction index (NCI) calculations. Furthermore, the different products of Ti, Zr, and Hf reactions with SiH4 are discussed in detail.

•MnO2@CNTs/Ni mesh electrode exhibits a high specific capacitance.•A symmetric supercapacitor (SSC) was assembled with enhanced performance.•The SSC delivers a wide working voltage and superior energy density and power density.Manganese dioxide is a promising electrode material for electrochemical supercapacitors, but its poor electronic conductivity (10−5∼10−6 S cm−1) limits the fast charge/discharge rate for practical applications. In the present work, we use the chemical vapor deposition (CVD) method to grow highly conductive carbon nanotube (CNT) networks on flexible Ni mesh, on which MnO2 nanoflake layers are deposited by a simple solution method, forming a hierarchical core-shell structure. Under the optimized mass loading, the as-fabricated MnO2 nanoflake@CNTs/Ni mesh electrode exhibits a high specific capacitance of 1072 F g−1 at 1 A g−1 in three-electrode configuration. Due to advantageous features of these core-shell electrodes (e.g., high conductivity, direct current path, structure stability), the as-assembled symmetric supercapacitor (SSC) based on MnO2@CNTs/Ni mesh has a wide working voltage (2.0 V) in 1 M Na2SO4 aqueous electrolyte. Finally an impressive energy density of 94.4 Wh kg−1 at 1000 W kg−1 and a high power density of 30.2 kW kg−1 at 33.6 Wh kg−1 have been achieved for the as-assembled SSC, which exhibits a great potential as a low-cost, high energy density and attractive wearable energy storage device.

•Four SiCeH4 isomers were identified based on SiD4 and DFT calculations.•The electron rich SiH3− facilitates the formation of hydrogen bridge bond.•Insertion H3CCeH structure was formed due to easier sp3 hybridization.Reactions of laser-ablated cerium atoms with silane were investigated by matrix isolation infrared spectroscopy and theoretical calculations. The reaction products, Si(μ-H)3CeH, H3SiCeH, H2Si(μ-H)CeH and HSi(μ-H)2CeH were identified on the basis of the SiD4 isotopic substitutions and DFT frequency calculations. In the solid argon or krypton matrix, the inserted H3SiCeH molecule was observed as initial product on deposition, which rearranged to hydrogen bridge species Si(μ-H)3CeH on follow-up annealing through H2Si(μ-H)CeH and HSi(μ-H)2CeH species. The SiHCe hydrogen bridge was investigated by NBO and ELF analysis. Calculation suggested that in Si(μ-H)3CeH molecule Ce atom donated one electron to Si atom, resulting in electron-rich SiH3 subunit, which was confirmed by ESP and AIM analysis. The increased basicity of SiH bond facilitates the formation of hydrogen bridge bond between Si and Ce. For comparison only insertion H3CCeH structure was obtained from the reaction of Ce atoms with CH4.Download high-res image (140KB)Download full-size image

A facile two-step method has been developed to synthesize 3D core/shell-structured composites (CNTs@Ni–Co–S) composed of ternary nickel cobalt sulfide nanosheets (Ni–Co–S) as the shell and carbon nanotubes (CNTs) as the core on a flexible Ni mesh (Ni@CNTs@Ni–Co–S). CNTs are in situ grown on a metallic Ni mesh via a chemical vapor deposition (CVD) method and further serve as the skeleton to deposit ultrathin Ni–Co–S nanosheets. Due to the intimate combination of highly conductive CNTs and high redox-active Ni–Co–S nanosheets, the as-prepared composite electrode delivers a high specific capacity of 222 mA h g−1 at 4 A g−1 and excellent rate capability (193 mA h g−1 at 50 A g−1). An advanced asymmetric supercapacitor (ASC) was designed using Ni@CNTs@Ni–Co–S as the positive electrode and carbon cloth @CNTs as the negative electrode in KOH solution. Our ASCs present a high energy density of 46.5 W h kg−1 at a power density of 800 W kg−1. Even at an ultra-high power density of 33.7 kW kg−1 (charging only for 2 s to 1.6 V), the ASCs can still demonstrate an energy density as high as 15.9 W h kg−1. Impressively, when charging to 3.4 V within 70 s, two ASCs assembled in series can effectively light up 10 light-emitting diodes (LEDs, lowest working voltage are 3.2 V) for more than 2 min or one single LED for around 50 min. These remarkable capacitive performances of Ni@CNTs@Ni–Co–S//CC@CNTs ASCs show great potential for application in supercapacitors, particularly in wearable devices.

The novel noble-gas complexes NgBeSO2 (Ng = Ne, Ar, Kr, Xe) have been prepared in the laser-evaporated beryllium atom reactions with SO2 in low-temperature matrixes. Doped with heavier noble gas, the guest (Ar, Kr, Xe) atom can substitute neon to form more stable complex. Infrared spectroscopy and theoretical calculations are used to confirm the band assignment. The dissociation energies are calculated at 0.9, 4.0, 4.7, and 6.0 kcal/mol for NeBeSO2, ArBeSO2, KrBeSO2, and XeBeSO2, respectively, at the CCSD(T) level. Quantum chemical calculations demonstrate that the Ng–Be bonds in NgBeSO2 could be formed by the combination of electron-donation and ion-induced dipole interactions. The Wiberg bond index (WBI) values of Ng–Be bonds and LOL (localized orbital locator) profile indicate that the Ng–Be bond exhibits a gradual increase in covalent character along Ne to Xe.

Reactions of laser-ablated boron atoms with SiH4 molecules gave silylene dihydroborate (H2BSiH2) in excess argon, which rearranged to silicon tetrahydroborate [Si(μ-H)2BH2] upon 300–350 nm irradiation. These reaction products were identified by functional group infrared frequencies, isotopic shifts, and comparison to infrared frequencies calculated by using density functional theory. It is found that H2BSiH2 has planar doublet ground state with electron-deficient B–Si double-bond character. Bonding analysis for Si(μ-H)2BH2 shows that 3c–2e B–H–Si bond is formed by accepting electrons donated from B–H σ bond.

[Ni(dddt)2]− (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) and [Ni(edo)2]− (edo = 5,6-dihydro-1,4-dioxine-2,3-dithiolate) are two donor-type nickel bis(dithiolene) complexes, with the tendency of donating low binding energy electrons. These two structurally similar complexes differ only with respect to the outer atoms in the ligand framework where the former has four S atoms while the latter has four O atoms. Herein, we report a negative ion photoelectron spectroscopy (NIPES) study on these two complexes to probe the electronic structures of the anions and their corresponding neutrals. The NIPE spectra exhibit the adiabatic electron detachment energy (ADE) or, equivalently, the electron affinity (EA) of the neutral [Ni(L)2]0 to be relatively low for this type of complexes, 2.780 and 2.375 eV for L = dddt and edo, respectively. The 0.4 eV difference in ADEs shows a significant substitution effect for sulfur in dddt by oxygen in edo, i.e., noninnocence of the ligands, which has decreased the electronic stability of [Ni(edo)2]− by lowering its electron binding energy by ∼0.4 eV. The observed substitution effect on gas-phase EA values correlates well with the measured redox potentials for [Ni(dddt)2]−/0 and [Ni(edo)2]−/0 in solutions. The singlet–triplet splitting (ΔEST) of [Ni(dddt)2]0 and [Ni(edo)2]0 is also determined from the spectra to be 0.57 and 0.53 eV, respectively. Accompanying DFT calculations and molecular orbital (MO) composition analyses show significant ligand contributions to the redox MOs and allow the components of the orbitals involved in each electronic transition and spectral assignments to be identified.

Asymmetric supercapacitors (ASCs) with carbon nanotube@nickel hydroxide nanosheet (CNT@Ni(OH)2) core–shell composites as positive electrodes and three-dimensional (3D) graphene networks (3DGNs) as negative electrodes were reported in aqueous KOH electrolyte. The CNT@Ni(OH)2 core–shell composites were prepared through a facile chemical bath deposition method, while 3DGNs were obtained by freeze-drying of graphene hydrogels. By virtue of their unique microstructures, superb electrochemical properties were achieved in a three-electrode system, e.g., 1136 F g−1 at 2 A g−1 for the CNT@Ni(OH)2 electrode within 0–0.5 V and 203 F g−1 at 1 A g−1 for the 3DGN electrode within −1–0 V. Benefiting from these merits, the as-fabricated CNT@Ni(OH)2//3DGN ASC showed a maximum energy density of 44.0 W h kg−1 at a power density of 800 W kg−1 and even retained 19.6 W h kg−1 at 16000 W kg−1 in the voltage region of 0–1.6 V.

•Carbon nanotubes@nickel oxide nanosheets (CNT@NiO) composites were prepared.•Porous carbon polyhedrons (PCPs) were obtained by carbonization of Zn-based MOFs.•An asymmetric supercapacitor CNT@NiO//PCPs was fabricated and investigated.•The asymmetric supercapacitor shows superior energy storage activity.Aqueous electrolyte based asymmetric supercapacitors (ASCs) has recently attracted increasing interest by virtue of their operation voltage and high ionic conductivity. Herein, we developed a novel ASC based on carbon nanotubes@nickel oxide nanosheets (CNT@NiO) core–shell composites as positive electrode and porous carbon polyhedrons (PCPs) as negative electrode in aqueous KOH solution as electrolyte. The CNT@NiO core–shell hybrids were prepared through a facile chemical bath deposition method followed by thermal annealing, while PCPs were obtained by direct carbonization of Zn-based metal-organic frameworks (MOFs). Owing to their unique microstructures, outstanding electrochemical properties have been achieved in three-electrode configuration, e.g., 996 F g−1 at 1 A g−1, 500 at 20 A g−1 for the CNT@NiO electrode within 0–0.5 V window, and 245 F g−1 at 1 A g−1 for the PCPs electrode within −1–0 V window. Resulting from these merits, the as-fabricated CNT@NiO//PCPs ASC exhibits maximum energy density of 25.4 Wh kg−1 at a power density of 400 W kg−1 and even remains 9.8 Wh kg−1 at 16,000 W kg−1 (a full charge–discharge within 4.4 s) in the wide voltage region of 0–1.6 V. More importantly, the CNT@NiO//PCPs asymmetric supercapacitor shows ultralong cycling stability, with 93% capacitance retention after 10,000 cycles.

•Natural cottons are activated using molten sodium at 800 °C.•Molten sodium activation is more effective than conventional KOH activation.•Asymmetric supercapacitors show outstanding performance.Combining high specific surface area (SSA) and superior electrical conductivity together at bulk state is very important for carbon materials in capacitive energy storage applications. Herein, by applying molten sodium metal to activate natural cotton at a relatively low processing temperature (800 °C), we have obtained hierarchically porous graphitic carbon fibers (HPGCFs) with SSA up to 1716 m2 g−1 and a high degree of graphitization in the bulk state. This is advantageous compared to amorphous carbon fibers obtained by conventional thermal annealing and KOH-activation. The obtained HPGCFs show remarkable energy storage capability (61% capacitance retention from 1 to 60 A g−1). To further increase the capacitance value, anthraquinone (AQ) molecules have been selected to functionalize HPGCFs via π–π stacking interactions. Asymmetric supercapacitors have been assembled using HPGCFs as the positive electrode and AQ-HPGCFs as the negative electrode in aqueous H2SO4 solution. The device presents a large energy density (19.3 Wh kg−1 in the applied potential range between 0 and 1.2 V) and ultrahigh power capability (up to 120 A g−1, a full charge–discharge within 0.8 s).

Laser-ablated Ti, Zr, and Hf atoms have been codeposited at 4 K with hydrogen sulfide in excess argon. The metal atoms insert into the S–H bond of hydrogen sulfide to form the HMSH, H2MS, and H2M(SH)2 molecules (M = Ti, Zr, Hf), which were identified on the basis of the D2S and H234S isotopic substitutions. The observed vibrational frequencies of these species were reproduced by B3LYP functional calculations. The reaction mechanisms have been proposed on the potential energy surface of the studied system to account for the formation of these molecules. We have made a theoretical prediction about the H2MS complexes dehydrogenation, which can provide a novel proposal for generating hydrogen from H2S.

Laser-ablated magnesium species were codeposited with SO2 in excess argon or neon on the substrate at 4 K. The reactions mainly produced Mg(η2-O2S), Mg(η2-O2S)2, Mg2(η2-O2S), OMg2(η2-SO), and Mg(η2-SO) complexes, which were identified by isotopic substitutions and density functional frequency calculations (B3LYP and BPW91). In addition, the collected infrared spectra suggest that the single Mg atoms could react with SO2 to form the Mg(η2-O2S) complex on annealing, which further reacts with SO2 to produce the Mg(η2-O2S)2 complex on irradiation. In contrast, the reactions of magnesium dimers lead to cleavage of the S═O bond in SO2 on irradiating. Structural and bonding characteristics of these generated complexes, which shed light on the different performances of single Mg atom and its dimer in their reactions with small molecules, are discussed.

A facile one-step strategy has been developed to prepare 3D graphene/VO2 nanobelt composite hydrogels, which can be readily scaled-up for mass production by using commercial V2O5 and graphene oxide as precursors. During the formation of the graphene/VO2 architecture, 1D VO2 nanobelts and 2D flexible graphene sheets are self-assembled to form interconnected porous microstructures through hydrogen bonding, which facilitates charge and ion transport in the electrode. Due to the hierarchical network framework and the pseudocapacitance contribution from VO2 nanobelts, the hybrid electrode demonstrates excellent capacitive performances. In the two-electrode configuration, the graphene/VO2 nanobelt composite hydrogel exhibits a specific capacitance of 426 F g−1 at 1 A g−1 in the potential range of −0.6 to 0.6 V, which greatly surpasses that of each individual counterpart (191 F g−1 and 243 F g−1 at 1 A g−1 for VO2 nanobelt and graphene hydrogel, respectively). The hybrid electrode also shows an improved rate capability and cycling stability, which is indicative of a positive synergistic effect of VO2 and graphene on the improvement of electrochemical performance. These findings reveal the importance and great potential of graphene composite hydrogels in the development of energy storage devices with high power and energy densities.

A pulsed laser deposition process using ozone as an oxidant is developed to grow NiO nanoparticles on highly conductive three-dimensional (3D) graphene foam (GF). The excellent electrical conductivity and interconnected pore structure of the hybrid NiO/GF electrode facilitate fast electron and ion transportation. The NiO/GF electrode displays a high specific capacitance (1225 F g−1 at 2 A g−1) and a superb rate capability (68% capacity retention at 100 A g−1). A novel asymmetric supercapacitor with high power and energy densities is successfully fabricated using NiO/GF as the positive electrode and hierarchical porous nitrogen-doped carbon nanotubes (HPNCNTs) as the negative electrode in aqueous KOH solution. Because of the high individual capacitive performance of NiO/GF and HPNCNTs, as well as the synergistic effect between the two electrodes, the asymmetric capacitor exhibits an excellent energy storage performance. At a voltage range from 0.0 to 1.4 V, an energy density of 32 W h kg−1 is achieved at a power density of 700 W kg−1. Even at a 2.8 s charge–discharge rate (42 kW kg−1), an energy density as high as 17 W h kg−1 is retained. Additionally, the NiO/GF//HPNCNT asymmetric supercapacitor exhibits excellent cycling durability, with 94% specific capacitance retained after 2000 cycles.

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10:1, to 5:1, 1:1 and 1:5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO1-1 h and MP/GO1-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm−1), annealed MP/GO1-1 h (A-MP/GO1-1 h, 7.48 × 10−2 S cm−1) and annealed MP/GO1-2 h (A-MP/GO1-2 h, 7.58 × 10−2 S cm−1). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g−1 for A-MP/GO1-1 h and A-MP/GO1-2 h, respectively.

Ethyl cellulose (EC) composites modified with 20.0 wt % polyethylenimine (PEI) (PEI/ECs) demonstrated effective hexavalent chromium, [Cr(VI)], removal from solutions with a wide pH range. For example, 4.0 mg/L Cr(VI) solution with a pH below 3.0 was completely purified by 3.0 g/L PEI/ECs within 5 min, much faster than the as-received EC (2 h) and activated carbon (several hours). These PEI/ECs adsorbents has overcome the low pH limitation of Cr(VI) removal; for example, 4.0 mg/L Cr(VI) solution with a pH of 11.0 was completely purified within 15 min. These adsorbents followed chemical adsorption as revealed from the pseudo-second-order kinetic study. These PEI/ECs following the isotherm Langmuir model have a maximum adsorption capacity of 36.8 mg/g, much higher than pure EC (12 mg/g), tetrabutylammonium-modified celluloses (16.67 mg/g), and magnetic carbon (16 mg/g). The reduction of Cr(VI) to Cr(III) by the oxidation of amine groups and hydroxyl groups of PEI/ECs was verified as the main mechanism for the Cr(VI) removal.Keywords: adsorption; Cr(VI) removal; ethyl cellulose (EC); kinetics; polyethylenimine (PEI); redox reaction

The TiN nanowire arrays (TiN NWAs) were prepared by hydrothermal treatment of Ti foil and subsequent nitridation through ammonia annealing, on which Ni(OH)2 was electrodeposited to form hierarchical TiN@Ni(OH)2 core/shell nanowire arrays (TiN@Ni(OH)2 NWAs). The electrochemical behaviors of TiN@Ni(OH)2 NWAs were measured by cyclic voltammetry (CV) and galvanostatic charge-discharge, which shows very high specific capacitance (2680 F g−1 at 6 A g−1 in 2 M KOH aqueous solution) and good rate capability (54% capacity retention at 60 A g−1). These results demonstrate that the TiN@Ni(OH)2 NWAs nanostructure is very promising for high performance supercapacitors.

The ethyl celluloses (ECs) modified with 5.0, 10.0, and 20.0 wt % polyaniline (PANI) (PANI/ECs) prepared by homogeneously mixing the EC and PANI formic acid solutions have demonstrated a superior hexavalent chromium (Cr(VI)) removal performance to that of pure EC. Having an increased Cr(VI) removal percentage with increased PANI loading, the PANI/ECs with 20.0% PANI loading were noticed to remove 2.0 mg/L Cr(VI) completely within 5 min, much faster than the pristine EC (>1 h). A chemical redox of Cr(VI) to Cr(III) by the active functional groups of PANI/ECs was revealed from the kinetic study. Meanwhile, isothermal study demonstrated a monolayer adsorption behavior following the Langmuir model with a calculated maximum absorption capacity of 19.49, 26.11, and 38.76 mg/g for the 5.0, 10.0, and 20.0 wt % PANI/ECs, much higher than that of EC (12.2 mg/g). The Cr(VI) removal mechanisms were interpreted considering the functional groups of both PANI and EC, the valence state fates of Cr(VI), and the variation of solution acidity.Keywords: Adsorption; Cellulose nanocomposites; Chromium removal; Polyaniline; Redox;

Coinage metal atom (Cu, Ag, Au) reactions with SO2 were investigated by matrix isolation infrared absorption spectroscopy and density functional theory electronic structure calculations. Both mononuclear complexes M(η1-SO2) (M = Ag, Au) and M(η2-O2S) (M = Ag, Cu) were observed during condensation in solid argon or neon. Interestingly, the silver containing mononuclear complexes are interconvertible; that is, visible light induces the isomerization of Ag(η1-SO2) to Ag(η2-O2S) and vice versa on annealing. However, there is no evidence of similar interconvertibility for the Cu(η2-O2S) and Au(η1-SO2) molecules. These different behaviors are discussed within the bonding considerations for all of the obtained products.

•Flexible graphene sheets decorated with Fe2O3 particles are self-assembled to form interconnected porous microstructures.•IR spectra show intramolecular hydrogen bonding is formed in grapheme/Fe2O3 composite hydrogels.•Graphene/Fe2O3 composite electrode exhibits ultrahigh specific capacitance of 908 F g−1 at 2 A g−1 within the potential range from −1.05 to −0.3 V, and outstanding rate capability (69% capacity retention at 50 A g−1).•Cycling performance is clearly much better for the graphene/Fe2O3 composite hydrogels than for pure Fe2O3 sample.To increase the energy density of supercapacitors to approach that of batteries, the current research is always directed towards the cathode materials, whereas the anode materials are rarely studied. In the present work, single-crystalline Fe2O3 nanoparticles directly grown on graphene hydrogels are investigated as high performance anode materials for supercapacitors. During the formation of the graphene/Fe2O3 composite hydrogels, flexible graphene sheets decorated with Fe2O3 particles are self-assembled to form interconnected porous microstructures with high specific surface area, which strongly facilitate charge and ion transport in the full electrode. Infrared spectra show that hydrogen bond is formed between C–OH on graphene hydrogels and Fe2O3. Benefits from the combined graphene hydrogels and Fe2O3 particles in such a unique structure are that the graphene/Fe2O3 composite electrode exhibits an ultrahigh specific capacitance of 908 F g−1 at 2 A g−1 within the potential range from −1.05 to −0.3 V, and an outstanding rate capability (69% capacity retention at 50 A g−1). Furthermore, the cycling performance is clearly much better for the graphene/Fe2O3 composite hydrogels than that for pure Fe2O3 sample. These findings open a new pathway to the design and fabrication of three-dimensional graphene hydrogel composites as anode materials in the development of high-performance energy-storage systems.Three-dimensional graphene/Fe2O3 composite hydrogels show ultrahigh specific capacitance and outstanding rate capability.

Anthraquinone (AQ) molecules were selected to decorate the lab-made hierarchical porous carbon nanotubes (HPCNTs) to obtain electrode materials (AQ-HPCNTs) for supercapacitors, which showed a remarkable capacitance increment in comparison with pure HPCNTs when tested in 1 M H2SO4 aqueous solution. At a current density of 1 A g–1, the AQ-HPCNTs (mass ratio 7:5) electrode showed an ultrahigh specific capacitance of 710 F g–1, which is much larger than that of the unmodified HPCNTs (304 F g–1). Even at a high discharge current density of 20 A g–1, the specific capacitance of the AQ-HPCNTs (mass ratio 7:5) electrode was still as high as 419 F g–1, indicating an excellent rate capability. Furthermore, all the AQ-HPCNTs electrodes exhibited a long cycle life. Electrochemical behaviors of AQ on the HPCNTs’ surface showed a double pair of redox peaks, which are appropriate for two types of π–π stacking interactions supported by infrared spectra. The excellent capacitive behaviors of the AQ-HPCNTs electrode materials are due to a strong positive synergistic effect between AQ and HPCNTs on the improvement of electrochemical performances.

Controllable synthesis and high yield of functional nanomaterials on conductive substrates are highly desirable for energy conversion and storage applications. In this work, two different porous NiCo2O4 nanoarchitectures (including nanowires and nanosheets) are directly grown on carbon cloth collectors, which display a structure-dependence in their capacitive behaviors. Our results show that the nanowire morphology exhibits higher specific capacitance and better cycling performance in the three-electrode configuration. The pseudocapacitive difference is related to the surface area and pore structure of NiCo2O4 nanocrystals. This comparison among different morphologies reveals a process–structure–property relationship in electrochemical energy storage.Keywords: capacitive behaviors; carbon cloth; nanosheets; nanowires; NiCo2O4;

A superior electrode for high-performance supercapacitors has been designed by growing homogeneous NiO nanoparticles on conductive Ni foam substrate through a facile two-step method. The preparation strategy involves the electrodeposition of nickel hydroxide precursor on Ni foam and subsequent low-temperature annealing process. These NiO nanoparticles are interconnected with each other, forming a loose network with a highly open and porous structure. This unique 3D NiO–Ni foam electrode manifests the electrolyte penetration and ion migration as well as large electroactive surface area. As a result, outstanding pseudocapacitive performance is achieved with a high specific capacitance (2558 F g−1 at 2 A g−1 in a potential window of 0.5 V) and excellent rate capability (70% capacity retention at 40 A g−1), which shows great potential in the development of high-performance energy-storage systems.

The aluminum doped cobalt oxide thin film was prepared through crossed-beam pulsed laser deposition (PLD) of aluminum and cobalt metals in the low-pressure O2/H2 atmosphere. The thin film was etched by NaOH to remove aluminum oxide and then cobalt oxide/hydroxide nanowall array film was obtained. The pseudocapacitive performances of the nanowall array film are tested by cyclic voltammetry (CV) and galvanostatic charge–discharge measurements in 1 M KOH aqueous solution. When deposited in the atmosphere of O2:H2 = 2:1, the thin film displays a high specific capacitance (690 F g–1) and a superb rate capability (75% capacitance retention from 1 A g–1 to 120 A g–1). In addition, excellent cycling stability is achieved for the film electrode and the specific capacitance degradation is only 0.3% after 1000 cycles.Highlights► Crossed-beam pulsed laser deposition of aluminum doped cobalt oxide thin film. ► Preparation of cobalt oxide/hydroxide nanowall array film by etching the aluminum doped cobalt oxide thin film. ► Cobalt oxide/hydroxide nanowall array film has superior capacitive behaviors.

Reactions of laser-ablated V, Nb and Ta atoms with SO2 in excess argon during condensation gave new absorptions in the MO stretching region, which were assigned to metal sulfide oxides SMO2 and anions SMO2− (M = V, Nb, Ta). The metal oxide complex OV(η2-SO) was also identified through the VO and the characteristic side-on coordinated S–O stretching modes. The assignments of major vibrational modes were confirmed by appropriate S18O2 and 34SO2 isotopic shifts, and density functional frequency calculations. DFT calculations were employed to study the behavior of reactions of Group V bare metal atoms with SO2, and a representative profile was derived which not only showed the preferred coordinating fashion of metal atoms but also tracked the path of S–O bond activation. The η2-O,O′ bridge coordinated complexes are preferred with energy decreases of ca. 50 kcal mol−1 for all three metals, which facilitate the activation of two S–O bonds in succession and finally direct the reaction to the most stable molecules SMO2 (M = V, Nb, Ta) along the potential energy surface (PES). Finally the SMO2 molecules capture electrons to give anions SMO2− with about 3.6 eV electron affinities based on DFT calculations.

A pulsed laser deposition process using ozone as an oxidant is developed to synthesize manganese oxide nanosheet arrays, which display excellent rate capability (52% capacity retention at 100 A g−1), comparable capacitance (337 F g−1 at 1 A g−1) and long cycle life (without degradation after 6000 cycles).

Highlights•Three new cyclic Pb–SO2 molecules were identified with η2-O,O bonded structure.•The observed infrared spectra were confirmed by DFT calculations.•Strong polarized covalent bond is formed between metal lead and SO2 ligand.Reactions of laser-ablated lead atoms with SO2 in excess argon produced three new molecules, cyclic Pb(SO2), Pb2(SO2) and Pb(SO2)2, all with η2-O,O bonded structure, which were identified by 34SO2 and S18O2 isotopic substitutions. The observed infrared spectra and molecular structures of three molecules were confirmed by density functional theoretical calculations. Mulliken and natural charge distributions indicate significant electron transfer from d orbitals of lead metal to SO2 ligand and lead–oxygen bond exhibits strong polarized covalent character.Graphical abstractCyclic lead–sulfur dioxide complexes were identified in low temperature matrix

Laser-ablated beryllium atom has been codeposited at 4 K with hydrogen sulfide in excess noble gas matrices. Four noble-gas compounds NgBeS (Ng = Ne, Ar, Kr, Xe) and the BeS2 molecule are identified on the basis of the S-34 isotopic substitution, DFT and CCSD(T) theoretical predictions, and a comparison of noble-gas substitution. The agreement between the experimental and calculated vibrational frequencies supports the identification of these molecules. The dissociation energies are calculated at 1.6, 12.6, 10.7, and 13.4 kcal/mol for NeBeS, ArBeS, KrBeS, and XeBeS, respectively, at the CCSD(T) level. The BeS Lewis acid molecule favors strong chemical binding between the Be and Ng atoms.

We report a remarkable transformation of multiwalled carbon nanotubes (MWCNTs) to curved graphene nanosheets (CGN) by the Hummers method. Through this simple process, MWCNTs can be cut and unzipped in the transverse and longitudinal directions, respectively. The as-obtained CGN possess the unique hybrid structure of 1D nanotube and 2D graphene. Such a particular structure together with the improved effective surface area affords high specific capacitance and good cycling stability during the charge–discharge process when used as supercapacitor electrodes. The electrochemical measurements show that CGN exhibit higher capacitive properties than pristine MWCNTs in three different types of aqueous electrolytes, 1 M KOH, 1 M H2SO4, and 1 M Na2SO4. A specific capacitance of as high as 256 F g–1 at a current density of 0.3 A g–1 is achieved over the CGN material. The improved capacitance may be attributed to high accessibility to electrolyte ions, extended defect density, and increased effective surface area. Meanwhile, this high-yield production of graphene from low cost MWCNTs is important for the scalable synthesis and industrial application of graphene. Furthermore, this novel CGN nanostructure could also be promisingly applied in many fields such as nanoelectronics, sensors, nanocomposites, batteries, and gas storage.Keywords: energy storage; graphene; multiwalled carbon nanotubes; supercapacitors; the Hummers method;

Infrared spectra of the matrix isolated OMS, OM(η2-SO), and OM(η2-SO)(η2-SO2) (M = Ti, Zr, Hf) molecules were observed following laser-ablated metal atom reactions with SO2 during condensation in solid argon and neon. The assignments for the major vibrational modes were confirmed by appropriate S18O2 and 34SO2 isotopic shifts, and density functional vibrational frequency calculations (B3LYP and BPW91). Bonding in the initial OM(η2-SO) reaction products and in the OM(η2-SO)(η2-SO2) adduct molecules with unusual chiral structures is discussed.

This work reports the pulsed laser reactive deposition of the NiO thin film by ablating nickel targets in low-pressure O2 atmosphere at room temperature. The electrode exhibits a porous structure, which facilitates ion transport in the electrode/electrolyte. When applied as an electrode, the porous NiO film exhibits the high specific capacitance (835 F g− 1 at 1 A g− 1). Meanwhile, the film exhibits a superb rate capability. At a very high current density of 40 A g− 1 there is more than 59% retention in the capacitance relative to 1 A g− 1. Furthermore, the excellent cycling performance (94% capacitance retention after 1000 cycles) is achieved for the film electrode. These results demonstrate that pulsed laser deposition (PLD) is a very promising technique for making the film electrodes for applications in electrochemical energy storage.Highlights► Laser ablated nickel atoms and ions react with O2 to form NiO thin film. ► The electrode exhibits a porous structure and demonstrates a respectable specific capacitance of 835 F g− 1. ► The NiO film structure exhibits a superb rate capability. ► The excellent cycling performance (without degradation after 1000 cycles) is achieved.

Laser-ablated tantalum atoms react with ammonia to form the metal-ammonia complexes Ta(NH3) and Ta(NH3)2 spontaneously on annealing. These complexes underwent photochemical rearrangement to form the imido molecule H2TaNH and amido complex H2Ta(NH2)2. The reaction products have been identified by isotopic substitutions as well as density functional theoretical frequency calculations. In addition, reaction mechanism of the possible reaction paths for these reactions is discussed.Graphical abstractThe tantalum atom reaction with one ammonia molecule to give imido complex H2TaNH and with two ammonia molecules to give amido complex H2Ta(NH2)2.Highlights► Tantalum atoms react with ammonia to form the metal-ammonia complexes. ► These complexes rearrange to form the imido and amido complexes. ► Isotopic substitutions and DFT frequency calculations are used for identification. ► Reaction mechanism is investigated theoretically.

Laser-ablated iridium atom has been codeposited at 4 K with acetylene in excess argon. The vinylidene IrCCH2, insertion product HIrCCH, and metallacycle complexes Ir-η2-(C2H2) and Ir-η2-(C2H2)2 are produced in present experiments and identified on the basis of the 13C2H2, C2D2, and mixed C2HD isotopic substitutions and the comparison with theoretical predictions. The agreement between the experimental and calculated vibrational frequencies supports the identification of these molecules. Two alternative reaction mechanism of formation of Ir═C═CH2 complex has been found on the potential energy surface of the studied system to account for the product formation. The conversion of acetylene to vinylidene on a Ir atom is exothermic by 3.4 kcal/mol based on the B3LYP functional calculations.

•We investigate SiH bond activation of SiH4 by Be atoms.•Excited Be(1P:2s12p1) atoms insert one SiH bond spontaneously.•HBeSiH3 rearranged to HBe(μ-H)3Si upon photolysis.•3c-2e bond was formed in HBe(μ-H)3Si through hydrogen bridged bond.Laser-ablated beryllium atoms have been reacted with silane molecules during condensation in excess neon and argon at 4 K. Absorptions due to HBeSiH3 and HBe(μ-H)3Si were observed and identified on the basis of isotopic IR spectroscopy, deuterium substitution with SiD4, and quantum chemical frequency calculations. The observed results show excited Be atom (1P1:2s12p1) can insert into SiH bond spontaneously and the insertion product rearranges to HBe(μ-H)3Si upon photolysis. The electron localization function (ELF) analysis suggests that 3c-2e hydrogen bridge bond (BeHSi) was formed by the donation of electrons for SiH σ bond to the empty p orbital of Be atom for HBe(μ-H)3Si molecule, which shows much difference from CH bond complexes.2D plot of the electron localization function in the plane of HBeSiH3 and HBe(μ-H)3Si.

Reactions of laser-ablated V, Nb and Ta atoms with SO2 in excess argon during condensation gave new absorptions in the MO stretching region, which were assigned to metal sulfide oxides SMO2 and anions SMO2− (M = V, Nb, Ta). The metal oxide complex OV(η2-SO) was also identified through the VO and the characteristic side-on coordinated S–O stretching modes. The assignments of major vibrational modes were confirmed by appropriate S18O2 and 34SO2 isotopic shifts, and density functional frequency calculations. DFT calculations were employed to study the behavior of reactions of Group V bare metal atoms with SO2, and a representative profile was derived which not only showed the preferred coordinating fashion of metal atoms but also tracked the path of S–O bond activation. The η2-O,O′ bridge coordinated complexes are preferred with energy decreases of ca. 50 kcal mol−1 for all three metals, which facilitate the activation of two S–O bonds in succession and finally direct the reaction to the most stable molecules SMO2 (M = V, Nb, Ta) along the potential energy surface (PES). Finally the SMO2 molecules capture electrons to give anions SMO2− with about 3.6 eV electron affinities based on DFT calculations.

Asymmetric supercapacitors (ASCs) with carbon nanotube@nickel hydroxide nanosheet (CNT@Ni(OH)2) core–shell composites as positive electrodes and three-dimensional (3D) graphene networks (3DGNs) as negative electrodes were reported in aqueous KOH electrolyte. The CNT@Ni(OH)2 core–shell composites were prepared through a facile chemical bath deposition method, while 3DGNs were obtained by freeze-drying of graphene hydrogels. By virtue of their unique microstructures, superb electrochemical properties were achieved in a three-electrode system, e.g., 1136 F g−1 at 2 A g−1 for the CNT@Ni(OH)2 electrode within 0–0.5 V and 203 F g−1 at 1 A g−1 for the 3DGN electrode within −1–0 V. Benefiting from these merits, the as-fabricated CNT@Ni(OH)2//3DGN ASC showed a maximum energy density of 44.0 W h kg−1 at a power density of 800 W kg−1 and even retained 19.6 W h kg−1 at 16000 W kg−1 in the voltage region of 0–1.6 V.

Coinage metal atom (Cu, Ag, Au) reactions with SO2 were investigated by matrix isolation infrared absorption spectroscopy and density functional theory electronic structure calculations. Both mononuclear complexes M(η1-SO2) (M = Ag, Au) and M(η2-O2S) (M = Ag, Cu) were observed during condensation in solid argon or neon. Interestingly, the silver containing mononuclear complexes are interconvertible; that is, visible light induces the isomerization of Ag(η1-SO2) to Ag(η2-O2S) and vice versa on annealing. However, there is no evidence of similar interconvertibility for the Cu(η2-O2S) and Au(η1-SO2) molecules. These different behaviors are discussed within the bonding considerations for all of the obtained products.

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10:1, to 5:1, 1:1 and 1:5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO1-1 h and MP/GO1-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm−1), annealed MP/GO1-1 h (A-MP/GO1-1 h, 7.48 × 10−2 S cm−1) and annealed MP/GO1-2 h (A-MP/GO1-2 h, 7.58 × 10−2 S cm−1). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g−1 for A-MP/GO1-1 h and A-MP/GO1-2 h, respectively.

A facile one-step strategy has been developed to prepare 3D graphene/VO2 nanobelt composite hydrogels, which can be readily scaled-up for mass production by using commercial V2O5 and graphene oxide as precursors. During the formation of the graphene/VO2 architecture, 1D VO2 nanobelts and 2D flexible graphene sheets are self-assembled to form interconnected porous microstructures through hydrogen bonding, which facilitates charge and ion transport in the electrode. Due to the hierarchical network framework and the pseudocapacitance contribution from VO2 nanobelts, the hybrid electrode demonstrates excellent capacitive performances. In the two-electrode configuration, the graphene/VO2 nanobelt composite hydrogel exhibits a specific capacitance of 426 F g−1 at 1 A g−1 in the potential range of −0.6 to 0.6 V, which greatly surpasses that of each individual counterpart (191 F g−1 and 243 F g−1 at 1 A g−1 for VO2 nanobelt and graphene hydrogel, respectively). The hybrid electrode also shows an improved rate capability and cycling stability, which is indicative of a positive synergistic effect of VO2 and graphene on the improvement of electrochemical performance. These findings reveal the importance and great potential of graphene composite hydrogels in the development of energy storage devices with high power and energy densities.

A facile two-step method has been developed to synthesize 3D core/shell-structured composites (CNTs@Ni–Co–S) composed of ternary nickel cobalt sulfide nanosheets (Ni–Co–S) as the shell and carbon nanotubes (CNTs) as the core on a flexible Ni mesh (Ni@CNTs@Ni–Co–S). CNTs are in situ grown on a metallic Ni mesh via a chemical vapor deposition (CVD) method and further serve as the skeleton to deposit ultrathin Ni–Co–S nanosheets. Due to the intimate combination of highly conductive CNTs and high redox-active Ni–Co–S nanosheets, the as-prepared composite electrode delivers a high specific capacity of 222 mA h g−1 at 4 A g−1 and excellent rate capability (193 mA h g−1 at 50 A g−1). An advanced asymmetric supercapacitor (ASC) was designed using Ni@CNTs@Ni–Co–S as the positive electrode and carbon cloth @CNTs as the negative electrode in KOH solution. Our ASCs present a high energy density of 46.5 W h kg−1 at a power density of 800 W kg−1. Even at an ultra-high power density of 33.7 kW kg−1 (charging only for 2 s to 1.6 V), the ASCs can still demonstrate an energy density as high as 15.9 W h kg−1. Impressively, when charging to 3.4 V within 70 s, two ASCs assembled in series can effectively light up 10 light-emitting diodes (LEDs, lowest working voltage are 3.2 V) for more than 2 min or one single LED for around 50 min. These remarkable capacitive performances of Ni@CNTs@Ni–Co–S//CC@CNTs ASCs show great potential for application in supercapacitors, particularly in wearable devices.

A pulsed laser deposition process using ozone as an oxidant is developed to grow NiO nanoparticles on highly conductive three-dimensional (3D) graphene foam (GF). The excellent electrical conductivity and interconnected pore structure of the hybrid NiO/GF electrode facilitate fast electron and ion transportation. The NiO/GF electrode displays a high specific capacitance (1225 F g−1 at 2 A g−1) and a superb rate capability (68% capacity retention at 100 A g−1). A novel asymmetric supercapacitor with high power and energy densities is successfully fabricated using NiO/GF as the positive electrode and hierarchical porous nitrogen-doped carbon nanotubes (HPNCNTs) as the negative electrode in aqueous KOH solution. Because of the high individual capacitive performance of NiO/GF and HPNCNTs, as well as the synergistic effect between the two electrodes, the asymmetric capacitor exhibits an excellent energy storage performance. At a voltage range from 0.0 to 1.4 V, an energy density of 32 W h kg−1 is achieved at a power density of 700 W kg−1. Even at a 2.8 s charge–discharge rate (42 kW kg−1), an energy density as high as 17 W h kg−1 is retained. Additionally, the NiO/GF//HPNCNT asymmetric supercapacitor exhibits excellent cycling durability, with 94% specific capacitance retained after 2000 cycles.